Cracking The Construction CO2 Conundrum

A little less country

China is a clear example of significant intra-country population shifts. There is considerable discussion regarding the country having reached its peak population, which is expected to remain stable before beginning to decline by 2035. It might be natural to deduce from this statistic that China’s needs will decline too, but while the population might not be growing, people are migrating internally from rural to urban areas in search of jobs and higher living standards. In 1980, 20% of China’s population lived in urban areas; by 2023, this figure had risen to 66%. By 2040, one rural policy expert and Chinese government advisor expects that an additional 400 million people will live in urban environments. And this trend is by no means specific to China. Across the world, from Nigeria to Indonesia, people are moving to urban areas in significant numbers.

Shifts are happening internationally too, with surging migration to markets emerging as new capitals of industry, such as the United Arab Emirates and the Kingdom of Saudi Arabia. This trend, coupled with rapid infrastructure expansion, is driving the need to build more, and faster, than ever before.

As urban areas continue to grow, there is a pressing need for new buildings to accommodate their increasing populations, alongside offices for employment, hospitals to maintain public health, and transportation infrastructure, including roads and railways. Additionally, these areas require a wide range of facilities, from sewage systems to sports stadium. To cope with these new demands, the world will need to embark on a massive, global building project equivalent to building an additional New York City every month. The best building material of sufficient strength and durability available at scale is concrete.

Alongside this increased demand for concrete is a global attention on sustainability and reduction in carbon emissions. The catch-22 is that the production of more concrete traditionally leads to higher CO₂ emissions due to its primary ingredient, cement, which has accounted for around 8% of global CO₂ emissions for at least the past six years. Given the need for more concrete to sustain global human development, how can the world ramp up production without simultaneously raising carbon emissions?

Flawed solutions

The construction industry has traditionally employed two main methods to dilute the amount of cement needed in concrete, thereby decreasing CO₂ emissions from the process.

The first is fly ash, which improves the consistency of concrete and often offers cost advantages. However, the time is ticking on its availability. Fly ash is produced at coal-fired power plants, which are increasingly hard to find. This year, the UK became the first G7 country to wean itself off coal-fired power with the closure of its Ratcliffe-on-Soar power plant. Although the pace of this transition varies across global markets, the trend, bar a few exceptions, is largely towards phasing out coal, not phasing it in.

Slag is the alternative to fly ash historically available to the construction industry. It also relies on a process involving coal, in the form of coke, to help reduce iron ore to molten iron; a crucial step in the steel-making process. Like fly ash, slag does offer some advantages in terms of performance, cost, and environmental impact, although the benefits to the environment will vary according to the process used. However, there are limitations to the availability of slag in places where there is no steel-making industry. For instance, the Kingdom of Saudi Arabia has ambitious gigaproject development plans as part of its Saudi Vision 2030 goals but does not produce steel using coal-fired furnaces, which means it does not generate slag. Consequently, producers operating there seeking to reduce CO₂ emissions from their concrete production will face various cost, currency, and logistical hurdles to secure a reliable supply of slag. Even if those challenges are overcome, it is difficult to argue that slag has a low CO₂ footprint, as it is a by-product of steel production, which has a significantly higher carbon footprint compared to cement. But what if there was an accessible local option that was also more sustainable?

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